1. Field of the Invention
The present invention relates to a method and an apparatus for marking an identification mark on a wafer, and more particularly, to a method for marking an identification mark to identify wafers by radiating a laser beam onto a predetermined portion on the wafer and an apparatus for performing the method.
2. Description of the Related Art
The elements of a semiconductor device are becoming more densely integrated to improve the processing speed and increase the memory capacity. A semiconductor device is generally manufactured by forming a multi-layer structure, including dielectric layers and conductive layers, through a sequence of film forming, pattern forming, and etching processes.
Among the many types of semiconductor devices, a MOS (metal oxide semiconductor) transistor is fabricated as follows. First, a wafer is divided into an active area and a field area on the basis of unit chips defined on the wafer. Then, a gate electrode and source/drain electrodes are formed in the active area. After an insulation layer is formed on the gate electrode, the insulation layer is etched so that a contact hole is formed for partially opening a surface portion of the wafer, where the source/drain electrodes are positioned. Then, a conductive layer is deposited in the contact hole and on the insulation layer. Thereafter, a predetermined portion of the conductive layer is etched so as to form a wiring pattern. A passivation layer is formed on the conductive layer, and a predetermined portion of the passivation layer is etched so as to define a connecting section for connecting the wiring to an external terminal.
Thereafter, the wafer is inspected for defects. If there are no defects, the wafer is cut into unit chips and a packaging process is implemented to complete the semiconductor device fabrication process.
It is important that the semiconductor device be fabricated by sequentially performing the unit processes in a predetermined order. If the unit processes are carried out in the wrong order, a failure or serious problem is likely to result, causing defects or degraded performance in the semiconductor device. Accordingly, the fabrication process must include a mechanism or process for checking the order of the unit processes when the wafer is fabricated. Identification marks are widely used, and they are marked onto a predetermined portion of the wafer to identify the wafer and allow operators to check the order of the unit processes. The identification mark is checked either by the operator or by an optical reader which may be conveyed to the operator. Since each unit process is carried out simultaneously with respect to twenty-five unit devices as one lot, the identification mark is also prepared on the basis of one lot of wafers.
Examples of identification marks are disclosed in U.S. Pat. No. 5,877,064 issued to Chang et al, and U.S. Pat. No. 5,956,596, issued to Jang et. al, U.S. Pat. No. 5,999,252, issued to Greisz, U.S. Pat. No. 6,004,405, issued to Oishi et. al, and U.S. Pat. No. 6,051,845, issued to Uritsky.
The identification mark is generally engraved on the wafer before the wafer is subjected to the unit processes, mainly by means of a laser beam. The identification mark is engraved onto a predetermined portion on the wafer by radiating the laser beam onto the predetermined portion on the wafer.
However, when the identification mark is engraved on the wafer by radiating the laser beam, contaminating particles may be created because the laser beam melts the surface of the wafer to create the mark. Accordingly, the wafer having the contaminating particles is subjected to the unit processes, which increases the likelihood of defects being generated during the processing steps.
In order to solve the above problem, U.S. Pat. No. 5,877,064 (""064) discloses a method for reducing the particles. According to the ""064 method, an identification mark is engraved at a bottom surface of a wafer, after the bottom surface has an oxide film formed thereon. A laser beam is radiated onto a predetermined portion of the bottom surface of the wafer, and the oxide film is then removed for obtaining the identification mark. However, though the above method can reduce the contaminating particles on the active surface of the wafer, since the identification mark is engraved at the bottom surface of the wafer, it is difficult to easily check the identification mark. In addition, the above method requires the formation and removal of an oxide film in order to obtain the identification mark, thereby adding costs, complexity and processing time to the manufacturing process.
In order to overcome the shortcomings of the prior art, it is an object of the present invention to provide a method for marking an identification mark on a wafer by radiating a laser beam, and thereafter easily removing any contaminating particles created during the marking process.
A second object of the present invention is to provide an apparatus for marking an identification mark on a wafer by radiating a laser beam, and thereafter easily removing any contaminating particles created during the marking process.
To achieve the first object of the present invention, there is provided a method for marking an identification mark on a wafer including engraving a wafer identification mark onto a predetermined portion of the wafer by radiating a laser beam onto the predetermined portion of the wafer. While the laser beam is being radiated, a gas is blown towards the predetermined portion of the wafer so as to blow particles away from the surface of the wafer, which particles were created on the surface of the wafer by radiating the laser beam. The gas, which is now mixed with the particles generated during the engraving process, is continually collected and exhausted during the engraving and blowing steps.
The predetermined portion of the wafer may be the flat zone of the wafer or a peripheral portion of the wafer where no patterns are formed. The laser beam is thus radiated onto the flat zone or the peripheral portion of the wafer so as to engrave the identification mark thereon. The laser beam is generated by means of an Nd/YAG laser operated in a dot matrix mode having a wavelength of 1064 nm. The Nd/YAG laser is widely used in various manufacturing industries.
The gas blows towards the wafer simultaneously with the radiation of the laser beam and keeps blowing after the radiation of the layer beam has been deactivated. Preferably, the gas keeps blowing for about 3 seconds after the radiation of the laser beam has been deactivated. The gas includes air, nitrogen gas, or a mixture thereof, and is blown onto the surface of the wafer at a oblique angle, preferably 20 to 40 degrees.
To achieve the second object of the present invention, there is provided an apparatus for marking a wafer identification mark on a wafer. The apparatus includes a supporting section for receiving and supporting the wafer, and a laser beam radiating section for engraving the wafer identification mark onto a predetermined portion of the wafer to identify the wafer. A blowing section has one end positioned adjacent to the wafer, and blows gas in a flow direction towards the predetermined portion of the wafer while the laser beam is being radiated so as to remove particles created on the surface of the wafer by radiating the laser beam.
The end of the blowing section comprises a nozzle oriented along the flow direction and positioned at an oblique angle relative to the surface of the wafer, wherein the gas flows though the nozzle and toward the surface of the wafer at an oblique angle of about 20 to 40 degrees.
A collecting and exhausting section, which is positioned adjacent to the surface of the wafer and confronts the flow direction of the blowing section, collects and exhausts the gas including the particles while the laser beam is being radiated. One end of the collecting and exhausting section has a cone-shaped end portion which is positioned adjacent to the surface of the wafer, and the other end comprises a suction member (e.g., a fan), providing a suction force for forcibly exhausting the gas.
A control section is electrically connected to the laser radiating section and the blowing section. The blowing section further includes-a solenoid valve for activating and deactivating the blowing of the gas. The control section operatively receives intensity data corresponding to a power applied to the laser beam radiating section, and the control section controls the activating and deactivating states of the solenoid valve based on the intensity data of the power. The solenoid valve is activated when the power is applied to the laser beam radiating section and is deactivated after a predetermined times lapses (e.g., 3 seconds) after the power applied to the laser beam radiating section is deactivated.
By using a marking apparatus and method as described above, particles created on the surface of the wafer can be effectively removed. Accordingly, the particles are prevented from sticking onto the surface on the wafer, so not only is the marking process performed in a stable manner, but also the failure of the device caused by the particles is prevented while subsequent processes are being performed.